function s1_generate_a_series_of_files(){
  for i in {1..100}; do
        echo $i > /tmp/new_file$i
    done
}
function s2_list_4_files_in_long_format_about_account_and_group(){
  ls -l /etc/{passwd,shadow,group,gshadow} | sort -d
}
function s3_find_items_related_to_given_username(){
  if [ "$#" -ne 1 ]; then
        echo "Usage: $0 <username>"
        return 1
  fi
  grep -h "$1" /etc/{passwd,shadow} | sort -d
}
function s4_find_items_related_to_given_group_name(){
  if [ "$#" -ne 1 ]; then
        echo "Usage: $0 <groupname>"
        return 1
  fi
  grep -h "$1" /etc/{group,gshadow} | sort -d
}
function s5_create_groups_for_given_group_names(){
  groupadd rnd && groupadd itoperation
}
function s6_create_users_and_set_their_group_as_required(){
  useradd -G rnd adam && useradd -G rnd bob \
           && useradd -G itoperation calvin && useradd -G itoperation david \
           && useradd -G rnd edward
}
function s7_change_users_shell(){
  usermod -s /usr/bin/sh adam && usermod -s /usr/bin/sh edward
}
function s8_set_password_change_policy(){
  for user in adam bob david calvin edward; do
        passwd -n 10 -x 60 -w 10 $user
  done
}
function s9_set_password_for_five_users(){
  if [ "$#" -ne 5 ]; then
        echo "Usage: $0 <adam_password> <bob_password> <calvin_password> <david_password> <edward_password>"
        return 1
  fi
  usernames=("adam" "bob" "calvin" "david" "edward")
  for i in {0..4}; do
        echo "${usernames[$i]}:$1" | chpasswd
        shift
  done
}
function s10_lock_bobs_password(){
  usermod -L bob
}
function s11_include_adam_into_wheel_group(){
  usermod -a -G wheel adam
}
function s12_change_files_permission(){
  for i in {1..33}; do
        chmod -R 640 /tmp/new_file$((3*i))
  done
}